Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $134.32   13.622%   $152.6171   $152.62   $152.60   $152.60  
  Purchase #2 $33.48   7.495%   $35.9893   $35.99   $36.00   $36.00  
  Purchase #3 $154.55   9.363%   $169.0205   $169.02   $169.00   $169.00  
  Purchase #4 $121.81   11.581%   $135.9168   $135.92   $135.90   $135.90  
  Purchase #5 $62.26   12.345%   $69.946   $69.95   $69.95   $69.90  
  Purchase #6 $15.57   10.246%   $17.1653   $17.17   $17.15   $17.20  
  Purchase #7 $158.90   6.565%   $169.3318   $169.33   $169.35   $169.30  
  7 purchase totals = $680.89       $749.9868   $750.00   $749.95   $749.90